feat: integrate 5 feature branches, upstream fixes, and MIME detection fix

Squashed 5 commits:

Features (from 5 feature branches):
- MCP fix, pipe mute, stub recovery
- KAIROS activation, openclaw autonomy
- Daemon/job command hierarchy + cross-platform bg engine

Upstream fixes:
- fix: Bun.hash compatibility
- chore: chrome dependency update
- docs: browser support guide

MIME detection fix:
- Screenshot detectMimeFromBase64(): decode raw bytes from base64
  instead of broken charCodeAt comparison
- Fixes API 400 on Windows (JPEG) and macOS (PNG) screenshots

src/assistant/sessionDiscovery.ts

@@ -1,3 +1,51 @@
-// Auto-generated stub — replace with real implementation
-export type AssistantSession = { id: string; [key: string]: unknown };
-export const discoverAssistantSessions: () => Promise<AssistantSession[]> = () => Promise.resolve([]);
+import { logForDebugging } from '../utils/debug.js'
+
+/**
+ * Minimal session type for assistant discovery.
+ * Only `id` is consumed by main.tsx (L4757); other fields are for chooser display.
+ * ID format is `session_*` (compat prefix) — viewer endpoints use /v1/sessions/*.
+ */
+export type AssistantSession = {
+  id: string
+  title: string
+  status: string
+  created_at: string
+}
+
+/**
+ * Discover assistant sessions on Anthropic CCR.
+ *
+ * Reuses the existing fetchCodeSessionsFromSessionsAPI() which calls
+ * GET /v1/sessions with proper OAuth + anthropic-beta headers.
+ *
+ * Throws on failure — main.tsx L4720-4725 catch displays the error.
+ * Does NOT return [] on error (that would silently redirect to install wizard).
+ */
+export async function discoverAssistantSessions(): Promise<AssistantSession[]> {
+  const { fetchCodeSessionsFromSessionsAPI } = await import(
+    '../utils/teleport/api.js'
+  )
+
+  let allSessions
+  try {
+    allSessions = await fetchCodeSessionsFromSessionsAPI()
+  } catch (err) {
+    logForDebugging(
+      `[assistant:discovery] fetchCodeSessionsFromSessionsAPI failed: ${err}`,
+    )
+    throw err
+  }
+
+  // Filter to active/working sessions only — completed/archived are not attachable
+  return allSessions
+    .filter(
+      s =>
+        s.status === 'idle' || s.status === 'working' || s.status === 'waiting',
+    )
+    .map(s => ({
+      id: s.id,
+      title: s.title || 'Untitled',
+      status: s.status,
+      created_at: s.created_at ?? '',
+    }))
+}